The invention relates generally to refractory compositions and more particularly to refractory compositions suitable for closing the tapholes of blast furnaces and the like.
Numerous compositions have been employed in the past for plugging blast furnace tapholes. These compositions generally comprise mixtures of a refractory filling material and a hardenable binding material. Prior art taphole mix compositions occasionally have been selected or modified in order to enhance or suppress one or more properties of the mix including the rate of hardening of the mix, the flowability of the mix or the nature of fumes given off during curing of the mix. Thus, it has been known in the past to employ natural binding materials, such as coal tar, synthetic resinous binding materials and mixtures thereof. It has also been known in the prior art to add various materials such as wetting agents or plasticizers to the composition.
For example, U.S. Pat. No. 4,022,739 issued May 10, 1977 to Bove discloses a composition for plugging blast furnace tapholes comprising about 70 to 85% of a mineral filler, and 15 to 30% of a hydrocarbon binder. The hydrocarbon binder consists of a thermosetting resin capable of preserving its stability at temperatures up to 200.degree. C. (392.degree. F.) and a hydrocarbon derivative having a temperature of initial distillation higher than 200.degree. C. (392.degree. F.). A secondary binder such as a pitch obtained by the distillation of tar or by the distillation of crude petroleum may also be included.
The hydrocarbon derivative employed as part of the binder in the Bove taphole mix may be (1) a non-paraffinic extract obtained by the treatment of the distillates of crude petroleum under vacuum with a selective solvent such as phenol, nitrobenzene or furfural or (2) a bituminous binder obtained by the direct distillation of crude petroleum and having an initial distillation temperature above 250.degree. C. at normal atmospheric pressure.
The respective portions of the resin and the hydrocarbon derivative are said to be selected so as to obtain at the time of use a hardening which is more or less rapid as a function of the characteristics and operation of the blast furnace. The percentage of hydrocarbon derivative in the mixed binder system is said to vary from 15% to 95%.
U.S. Pat. No. 4,072,531 issued Feb. 7, 1978 to Funabiki et al. also discloses a plugging composition for blast furnace tapholes comprising a refractory filler, a lignin-modified phenolic resin binder and a wetting agent such as ethylene glycol, diethylene glycol, propylene glycol, polyethylene glycol or plasticizers, such as dioctylphthalate or tricresyl phosphate, and the like. The wetting agent is added in an amount sufficient to form a clay-like mass capable of being injected into a blast furnace taphole by means of a "mud gun" or similar apparatus and typically is present in amounts from about 0.5 to about 20 parts by weight per 100 parts of refractory filler.
Both Bove and Funabiki et al. are representative of efforts to improve upon the coal tar binder sometimes employed in taphole mix compositions. While binders not containing coal tar may be advantageous in a number of respects, such substitutions generally have the disadvantage of higher cost of materials.
U.S. Pat. No. 2,841,502 issued July 1, 1958 to West et al. discloses a taphole mix comprising a refractory filler and thermal asphalt, the latter being defined as an oleaginous material obtained by the thermal cracking of heavy oils such as cycle oils and reduced crudes containing a high proportion of fused ring aromatics. The thermal asphalt is employed in amounts from about 2 to about 15%.
As can be seen from the foregoing, formulators of prior art taphole mix compositions have occasionally recognized the need to adjust the flowability of the mixture by the addition of materials which have a plasticizing effect on the mixture. Such plasticizing materials have also been employed in other tar bonded refractory materials. For example, U.S. Pat. No. 3,141,783 issued July 21, 1964 to Weaver discloses the use of hydrogenated hydrocarbons such as hydrogenated sperm oil to enhance the flowability and plasticity of refractory lining materials containing a refractory filler and a tar binder.
Formerly, in coal tar bonded taphole mixes designed for use in small blast furnaces, the mix had to be softened through the use of creosotes or light coal tar oils or added amounts of tar. In use, when these "soft" taphole mixes are applied to a taphole and the mud gun is held in place for 20 to 30 minutes, the mixes harden in the nozzle of the gun. This requires very careful cleaning of the nozzle after each usage to prevent serious application difficulties and, in general, leads to a higher usage rate of taphole mix.